High temperature clip cushion

ABSTRACT

A process and composition of matter for preparing an improved clip cushion product having tighter dimensional control, better consistency of composition, higher heat resistance, better crack resistance, less abrasive, and lower weight loss at high temperature.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] Not Applicable.

FEDERALLY SPONSORED RESEARCH

[0002] Not Applicable.

MICRO FISCHE APPENDIX

[0003] Not Applicable.

BACKGROUND OF THE INVENTION

[0004] This clip cushion relates to fasteners, and specifically to theaerospace industry where high temperatures are experienced.

[0005] The areas around rocket motors and jet engines experiencetemperature extremes in the 450° F. to 600° F. range, and above.Assemblies in these areas need to have other parts attached to them. Aprime example would be a hydraulic or fuel line attached to or near anengine. Hence, a hollow metal tube needs to be attached to the engine oranother object. If a metal strap were used to fasten the metal tube,problems would occur. Fastening one metal part to another causesproblems if vibration and movement between parts occur. Also, the metalparts may abrade each other and cause a hole in the tube.

[0006] The solution of the 1950's was to use a non-metallic cushionbetween the strap and the tube. These parts are usually referred to asclamp cushions or clip cushions.

[0007] Aerospace companies approved and wrote specifications around anasbestos textile based product, which was coated withpolytetrafluoroethylene dispersion and then dried, formed, sintered, andmachined. The entire process took about ten separate steps.

[0008] Asbestos in grades AA and AAA and Teflon were serviceable at 600°F. The Teflon coating allowed for the tube to slide within the strapduring movement. Vibration and abrasion were reduced by the non-metalliccushion effect. However, when the Teflon (i.e. polytetrafluoroethylene)coating wore down, the asbestos fibers caused abrasion due to their highmodulus.

[0009] However, the use of asbestos came under attack by variousgovernment agencies and the public in general.

[0010] For whatever reason, the aerospace community eliminated asbestosbeginning with product approvals in 1986.

[0011] The second solution to this fastening problem was to use anon-asbestos based textile product coated with Teflon as thereplacement. The non-asbestos textile was based on Nomex, Kevlar,fiberglass, and polybenzimidazole (i.e. PBI). The process was verysimilar and also took about ten steps.

[0012] However, the replacement product has problem areas. First,Kevlar, Nomex, and PBI are not rated to 600° F. They are rated at 355°F., 500° F., and 500° F. respectively as reported in “MaterialEngineering—Materials Selector 1989.”

[0013] Second, Kevlar is high modulus and is abrasive.

[0014] Third, when a textile-based product is machined, the yarn endsare cut. When this is subsequently bent, the yarn ends have a desire toseparate due to stress. This causes a crack between yarn ends whichquestions product reliability as to whether the crack will propagateover time or not.

[0015] Fourth, a ten-step process involving water based dispersions andtextile methods can be difficult to control from a compositionconsistency and dimensional control viewpoints.

[0016] Current specifications on the non-asbestos based textile productinclude: A50TF232 General Electric Aircraft BPS-C-155 Boeing AircraftPWA 484 Pratt and Whitney CPW 437 Pratt and Whitney EMS-24215 AllisonAMS 3677 Aerospace Material Specification

SUMMARY OF THE INVENTION

[0017] The invention is an improved product for high temperature clipcushions using an improved composition of matter and an improvedprocess.

[0018] The improved process reduces the process steps from about ten totwo: mix the powders and ram extrude to size in a Teflon processingextruder. Process inconsistencies are reduced and dimensional values aremore tightly controlled through the die forming process.

[0019] The improved composition of matter is based on:

[0020] Teflon powder (PTFE or chemically modified PTFE*)

[0021] Glass bubbles and/or beads (micro version)

[0022] High temperature pigments (if needed for coding)

[0023] NXT70 by Dupont and TFM by Dyneon for example.

[0024] All of these materials are rated for a minimal weight loss andtensile reduction up to 650° F. The Teflon may experience some softeningaround 635° F. Excursions to 700° F. are believed possible with minimalproblems. Trials on a 70% Teflon and 30% glass bubbles or beads showed aweight loss after 24 hours at 600° F. of 0.1% and 0.04% respectively.This compares to a typical 1.00% loss on the standard textile basedproduct.

[0025] Abrasion should be improved by the elimination of Kevlar but notests have been done.

[0026] The “cracking” phenomenon between yarn ends of a textile productis eliminated by the use of a homogeneous blend of powders. Bend testson the materials subjected to 600° F. for 24 hours showed fullflexibility and no cracking after being bent on themselves (i.e. 180° orfolded on themselves). The normal test is to bend around a ¼″ diameterrod and check for cracks.

DESCRIPTION OF THE DRAWINGS

[0027]FIG. 1 is a side view of a tube fastened to a support with a clipcushion in place.

[0028]FIG. 2 is a cross sectional view showing a typical clip cushionconfiguration.

[0029]FIG. 3 is a cross sectional view showing another typical clipcushion configuration.

DESCRIPTION OF THE INVENTION

[0030] The composition of matter has already been discussed. It is newand novel in that it uses powder extrusion instead of a textile basedproduct; it uses a new composition of matter, and it is a new use forpowder technology.

[0031] It is non-obvious in that textile based material has been usedfor 50 years, and omission of some previously used materials provideproduct improvements.

[0032] The process of ram extrusion or compression molding of Teflonpowders is well known. The basic process is to blend powders and thenram extrude or compression mold them. Any person skilled in the art ofTeflon molding or ram extrusion could make the final product. Theinvention is not the process but using the process in a field in whichit has not been used before.

I claim:
 1. A process for preparing a clip cushion product havingtighter dimensional control and better consistency of composition thanconventional polytetrafluoroethylene dispersion dipped and sinteredtextile products, the method comprising: a. Blending a mixturecomprising polytetrafluoroethylene powder and glass micro bubbles. b.Extruding the blend into the desired profile.
 2. A process according toclaim 1 wherein the steps of blending the mixture comprisespolytetrafluoroethylene powder and glass micro beads.
 3. A processaccording to claim 1 or claim 2 wherein the step of extruding the blendcomprises compression molding the blend into the desired shape
 4. A clipcushion material comprising a mixture of polytetrafluoroethylene powderand glass micro bubbles whereby a more heat resistant, better crackresistant, less abrasive, and lower weight loss at 600° F. clip cushionwill be provided.
 5. A material according to claim 4 wherein the mixturecomprises polytetrafluoroethylene powder and glass micro beads.